FIG. 1 shows an exemplary network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system to which a related art and the present invention are applied. The E-UMTS system is a system that has evolved from the UMTS system, and its standardization work is currently being performed by the 3GPP standards organization. The E-UMTS system can also be referred to as a Long-Term Evolution (LTE) system.
The E-UMTS network can roughly be divided into an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a Core Network (CN). The E-UTRAN generally comprises a terminal (i.e., User Equipment (UE)), a base station (i.e., eNode B), and an Access Gateway (AG) that is located at an end of the E-UMTS network and connects with one or more external networks. The AG may be divided into a part for processing user traffic and a part for handling control traffic. Here, an AG for processing new user traffic and an AG for processing control traffic can be communicated with each other by using a new interface. One eNode B may have one or more cells. An interface for transmitting the user traffic or the control traffic may be used among the eNode Bs. The CN may comprise an AG, nodes for user registration of other UEs, and the like. An interface may be used to distinguish the E-UTRAN and the CN from each other.
Radio interface protocol layers between the terminal and the network can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) standard model widely known in communications systems. A physical layer belonging to the first layer provides an information transfer service using a physical channel. A Radio Resource Control (RRC) layer located at the lowest portion of the third layer controls radio resources between the terminal and the network. For this purpose, the RRC layer allows RRC messages to be exchanged between the terminal and the network.
FIGS. 2 and 3 show radio interface protocol architecture between a terminal and E-UTRAN based on 3GPP radio access network standards. Particularly, FIG. 2 shows radio protocol architecture in a control plane, and FIG. 3 shows radio protocol architecture in a user plane.
The radio interface protocol in FIGS. 2 and 3 has horizontal layers comprising a physical layer, a data link layer and a network layer, and has vertical planes comprising a user plane for transmitting user traffic and a control plane for transmitting control signals. The protocol layers in FIGS. 2 and 3 can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) standard model widely known in communications systems. Hereinafter, each layer in the radio protocol control plane in FIG. 2 and a radio protocol user plane in FIG. 3 will be described.
A first layer, as a physical layer, provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to its upper layer, called a Medium Access Control (MAC) layer, via a transport channel. The MAC layer and the physical layer exchange data via the transport channel. Data is transferred via a physical channel between different physical layers, namely, between the physical layer of a transmitting side and the physical layer of a receiving side. The physical channel is modulated based on an Orthogonal Frequency Division Multiplexing (OFDM) technique, and utilizes time and frequency as radio resources.
The MAC layer located at the second layer provides a service to an upper layer, called a Radio Link Control (RLC) layer, via a logical channel. The RLC layer of the second layer supports reliable data transmissions. The function of the RLC layer may be implemented as a functional block in the MAC layer. In this case, the RLC layer may not exist. A Packet Data Convergence Protocol (PDCP) layer of the second layer, in the radio protocol user plane, is used to efficiently transmit IP packets, such as IPv4 or IPv6, on a radio interface with a relatively narrow bandwidth. For this purpose, the PDCP layer reduces the size of an IP packet header which is relatively great in size and includes unnecessary control information, namely, a function called header compression is performed.
A Radio Resource Control (RRC) layer located at the lowest portion of the third layer is only defined in the control plane. The RRC layer controls logical channels, transport channels and physical channels in relation to establishment, re-configuration and release of Radio Bearers (RBs). Here, the RB signifies a service provided by the second layer for data transmissions between the terminal and the E-UTRAN. If an RRC connection is established between the RRC layer of the terminal and the RRC layer of the radio network, the terminal is in the RRC connected mode. Otherwise, the terminal is in an RRC idle mode.
A Non-Access Stratum (NAS) layer located at an upper portion of the RRC layer performs functions, such as session management, mobility management and the like.
One cell constructing an eNB is set to one of bandwidths of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 20 MHz and the like, so as to provide downlink or uplink transmission services to multiple terminals. Here, different cells may be set to provide different bandwidths.
Downlink transport channels for transmitting data from a network to a terminal may comprise a Broadcast Channel (BCH) for transmitting system information, a Paging Channel (PCH) for transmitting paging messages and a downlink Shared Channel (SCH) for transmitting other user traffic or control messages. Traffic or control messages of a downlink point-to-multipoint service (multicast or broadcast service) may be transmitted either via a downlink SCH, or via a separate downlink Multicast Channel (MCH). In addition, uplink transport channels for transmitting data from a terminal to a network may comprise a Random Access Channel (RACH) for transmitting an initial control message and an uplink Shared Channel (SCH) for transmitting user traffic or control messages.
Logical channels which are located at an upper portion of transport channels and mapped to the transport channels include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a MBMS point-to-multipoint Control Channel/Multicast Control Channel (MCCH), a MBMS point-to-multipoint Traffic Channel/Multicast Traffic Channel (MTCH), and the like.
FIG. 4 shows a transmission on a control channel according to the related art.
A physical channel is composed of multiple sub-frames arranged on a time axis and multiple sub-carriers arranged on a frequency axis. Here, a single sub-frame includes a plurality of symbols on the time axis. One sub-frame is composed of a plurality of resource blocks, each of which includes a plurality of symbols and a plurality of sub-carriers. Also, each sub-frame can use particular sub-carriers of particular symbols (e.g., a first symbol) at the corresponding sub-frame for a Physical Downlink Control Channel (PDCCH), namely, a L1/L2 control channel. One sub-frame is a time duration of 0.5 ms. A Transmission Time Interval (TTI) as a unit time for which data is transmitted is 1 ms corresponding to two sub-frames.
FIG. 5 shows an exemplary view of a related art channel structure for a paging channel transmission. In general, a terminal may perform a DRX (Discontinuous Reception) operation in order to reduce power consumption by the terminal when it receives a paging message. To do this, a network configures a plurality of paging occasion for every time period, which so called a paging DRX cycle, and a particular terminal can obtain the paging message by receiving a particular paging occasion. Here, the terminal does not receive any paging channel within any other time except the particular paging occasion and the paging occasion is corresponding to a TTI (Transmission Time Interval).
FIG. 6 shows an exemplary paging process in a related art. As illustrated in FIG. 6, a sGW (serving gateway) pages a MME (mobility management entity) when data or paging is received from an Internet network or PSTN (public switched transfer/telephone network). The MME configures a paging message and then transmits the paging message to an eNB. The eNB then transmit the paging message to a terminal (UE, MS). After the paging message received by the terminal, the terminal performs a RRC connection and transmits a NAS message. After that, the core network performs a call setup process with the terminal once the NAS message is received from the terminal.
As it can be seen from the paging process illustrated in FIG. 6, in related art, too many steps are existed for completing the paging process. In particular, the paging message that transmitted from the MME to the eNB only includes information related to a terminal identifier, a paging period, and the like. Therefore, even after the eNB receives a request for the RRC connection, the eNB does not exactly know which radio resource should be assigned to the terminal or which cell the terminal should be move.
FIG. 7 shows another exemplary paging process in a related art. As illustrated in FIG. 7, the paging message is transmitted from the MME to the eNB. After receiving the paging message, the eNB transmits the paging message to the UE, and then the UE transmits a NAS message to the MME after performing a RRC connection process. After receiving the NAS message, the MME establishes a S1 connection with the eNB, and then transmits a response in response to the NAS message. The eNB performs a handover preparation based on information received from the MME, and then transmits a handover command to the UE. After UE is moved to other cell according to the handover command, call setup process can be continued.
In related art, there are many steps existed in the paging process, thereby causing a complexity. Further, there is great drawback causing a delayed call setup because the eNB never receives any information related to the UE during the paging process in the related art.